Waveguide circulator having single gyromagnetic element

ABSTRACT

A three-port waveguide circulator has three waveguide arms meeting at a common junction. A gyromagnetic element is centrally situated at the junction and is subjected to the influence of a magnetic field during operation of the circulator. An appreciable saving in gyromagnetic material is effected by making the gyromagnetic element approximately one quarter wavelength long at the center frequency of the band and mounting that element upon a pedestal that rises from a transformer plate. Both the transformer plate and the pedestal effect a narrowing in the height of the waveguide. One face of the gyromagnetic element is short circuited by the pedestal whereas the opposite face is open-circuited by a dielectric gap between it and the waveguide wall. To permit the thickness of the gap to be adjusted the pedestal or a portion of the waveguide wall directly opposite the gyromagnetic element can be made movable. To tune the in-phase mode without appreciably affecting the counterrotating modes, a thin tuning post is provided that extends into the dielectric gap from the waveguide wall opposite the open-circuited face of the gyromagnetic element.

United States Patent Helszajn WAVEGUIDE CIRCULATOR HAVING SINGLE GYROMAGNETIC ELEMENT [75] Inventor: Joseph Helszajn, Edinburgh,

Scotland [73] Assignee: Microwave Development Laboratories, Inc., Needham-Heights, Mass.

[22] Filed: Mar. 15, 1974 [21] Appl. No.: 451,510

[30] Foreign Application Priority Data Mar. 26, 1973 United Kingdom 14566/73 [52] US. Cl 333/1.1; 333/9 [51] Int. Cl. HOlp 1/32 [58] Field of Search 333/1.l

[56] References Cited UNITED STATES PATENTS 3,015,787 1/1962 Allin et a1, 333/].1 3,104,361 9/1963 Leetmaa et a1. H 333/].1

3,231,835 1/1966 Nielsen et a1. t v 333/l.1 3,670,134 6/1972 Bucksbaum a. 333/11 X Primary Examiner-Paul L. Gensler Attorney, Agenr, 0r Firm-Wolf, Greenfield & Sacks CDNDUCTIVE PEDESTAL TRANSFORMER PLATE [57] ABSTRACT A three-port waveguide circulator has three waveguide arms meeting at a common junction. A gyromagnetic element is centrally situated at the junction and is subjected to the influence of a magnetic field during operation of the circulator. An appreciable saving in gyromagnetic material is effected by making the gyromagnetic element approximately one quarter wavelength long at the center frequency of the band and mounting that element upon a pedestal that rises from a transformer plate. Both the transformer plate and the pedestal effect a narrowing in the height of the waveguide. One face of the gyromagnetic element is short circuited by the pedestal whereas the opposite face is open-circuited by a dielectric gap between it and the waveguide wall. To permit the thickness of the gap to be adjusted the pedestal or a portion of the waveguide wall directly opposite the gyromugnetic element can be made movable To tune the in-phase mode without appreciably affecting the counterrotating modes, a thin tuning post is provided that extends into the dielectric gap from the waveguide wall opposite the open-circuited face of the gyromagnetic element.

4 Claims, 7 Drawing Figures orm B OUARTERWAVE GYROMAGNETIC ELEMENT arm A PATENTEU MAY 2 7 ms SHEET Tl R A R w R P FIG 2 PRIOR ART OUARTERWAVE GYROMAGNETIG B m r O ELEMENT 'GrmA WAVEGUIDE CIRCULATOR HAVING SINGLE GYROMAGNETIC ELEMENT This invention relates in general to apparatus for non-reciprocal transmission of electromagnetic wave energy and more particularly, the invention pertains to broadband waveguide y-junction circulators.

DISCUSSION OF THE PRIOR ART The conventional three port waveguide symmetrical waveguide circulator employs three waveguide arms that are arranged at angles of I20 with respect to one another and meet at a common junction. Centrally disposed at the junction are one or more gyromagnetic members which are situated to preserve the symmetry of the junction. The gyromagnetic members are subjected to the influence of a magnetic field in the operation of the circulator to cause the device to be a nonreciprocal transmitter of electromagnetic wave energy propagating in the waveguide. To improve the operating characteristics of the symmetrical y-junction circulator. modifications in the size and shape of the gyromagnetic members and in the matching the impedance of those members to the remainder of the structure have been made. The improved circulators have, in general, preserved the symmetry of the junction and have required gyromagnetic members of appreciable volume.

US. Pat. No. 3,104,361 granted to J. G. Leetmaa, et al, discloses a circulator having a triangular gyromagnetic member situated between a pair of triangular transformer plates. The gyromagnetic member is entirely with the junction and the apexes of the triangular transformer plates extend into the waveguide arms to provide an impedance match for the gyromagnetic member. The arrangement preserves the symmetry of the junction while providing an impedance matching structure that is asserted to be less frequency sensitive than conventional impedance transformers.

US. Pat. No. 3,684,983. granted to J. J. Cotter, et a], discloses a circulator employing a pair of triangular gyromagnetic members separated by an interposed Teflon member. The gyromagnetic members are disposed between a pair of transition elements that reduce the height of the waveguide in two steps to provide impedance matching. The Cotter, et al circulator preserves the symmetry of the junction but its construction is somewhat more critical than the Leetmaa, et al circulator because Cotter, et al uses two gyromagnetic members that must be maintained in alignment to preserve the symmetry of the junction whereas Leetmaa, et al employs a single gyromagnetic member. However, even in the Leetmaa. et al device, the upper and lower transformer plates must be maintained in alignment as well as the dielectric supports between which the gyromagnetic member is sandwiched.

SUMMARY OF THE INVENTION The invention resides in an improved three-port waveguide circulator of simplified construction that requires but a single gyromagnetic element approximately one quarter wavelength long measured in the gyromagnetic material. Only one transformer plate is required although two transformer plates may be used. To minimize the cost of manufacture and avoid the necessity for aligning two transformer plates, a one transformer plate construction is preferred. The gyromagnetic member is disposed at the center of the junction with one face spaced from the waveguide wall by a dielectric gap which can be made adjustable to facilitate tuning of the device. The opposite face of the gyromagnetic member is disposed upon a conductive member so that that face is short circuited whereas the obverse face is open circuited at the dielectric gap. Because of the asymmetrical arrangement of the gyromagnetic member, an additional advantage is gained in that the higher order modes are shifted to a portion of the frequency spectrum outside the band of intended operation of the circulator. The invention, because it employs a single quarter wave gyromagnetic element. permits a reduction in weight to be achieved over conventional circulators which employ three quarter wavelength or one half wavelength gyromagnetic elements. Moreover, an appreciable saving in cost can be realized by the reduction in volume of the ferrite or garnet gyro magnetic material needed for a quarter wavelength element, compared to the material needed for a half wave or three quarter wave length element.

THE DRAWINGS The invention, both as to its construction and its mode of operation, can be better understood from the detailed description that follows when it is considered in conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of a conventional prior art waveguide y-junction circulator in which interior components are depicted in phantom;

FIG. 2 is a cross-sectional view in elevation taken along the line 2-2 in FIG. I;

FIG. 3 is a perspective view of the preferred embodiment of the inventor in which parts are broken away to expose the interior of the circulator;

FIG. 4 is a cross-sectional view in elevation of the preferred embodiment of the invention taken along the line 4-4 in FIG. 3;

FIG. 5 indicates dimensions to be considered in the construction of the preferred embodiment;

FIG. 6 depicts a modification of the preferred embodiment which permits independent tuning of the inphase mode by a central tuning post;

FIG. 7 depicts an embodiment of the invention em- P y ng a triangular gyromagnetic element and a triangular transformer plate.

DETAILED DESCRIPTION FIG. 1 depicts a prior art waveguide y-junction circulater having three waveguide arms AB. and C meeting at a common junction. Centrally disposed at the junction are a pair of gyromagnetic disks 1 and 2, which for ease of exposition are assumed to be of ferrite exhibitlng y agnetic properties. The ferrite disks are identical in diameter and thickness and are separated by a gap that in some conventional circulators is filled with a dielectric material. The ferrite disks are disposed between a pair of Circular transformer plates 3 and 4 that match the impedance of the ferrite desks to the waveguide structure. In the operation of the circulator, the ferrite disks are subjected to the influence of unidirectional magnetic field. represented in FIG. I y the arrow designated H The magnetic field can be established by one or more permanent magnets or may be set up by an electromagnet having the ferrite disks between its pole pieces.

Electromagnetic wave energy entering waveguide arm A propagates to the junction and because of the gyromagnetic properties of the ferrite disks, substantially all the energy is directed into arm B. In the ideal waveguide circulator, all the wave energy enters arm B and none enters arm C. The circulator is not a reciprocal transmitter because wave energy entering arm B is directed into arm C and not into arm A.

By changing the direction of magnetic field H the circulator can be operated as a switch in as much as a reversal in direction of that magnetic field causes electromagnetic wave energy entering arm A to be directed into arm C rather than into arm B.

FIG. 2 shows a cross-section of the prior art circulator taken along the plane 2-2 in FIG. I. The ferrite disks 1, 2 must be maintained in alignment as well as the transformer plates 3, 4, to preserve the symmetry of the junction. Construction of the circulator requires relatively precise dimensional control as there usually is no provision for adjustment of the gap between the ferrite disks after the device is assembled. Commonly, however, capacitive tuning screws, as shown in U.S. Pat. No. 3,593,210, are provided in each waveguide arm to facilitate tuning.

FIG. 3 depicts the preferred embodiment of the invention with part of the waveguide top wall broken away to expose the interior of the circulator. In the FIG. 3 arrangement the gyromagnetie element 5 is a disk of a material such as ferrite of garnet exhibiting gyromagnetic properties. The diameter of the disk is approximately a quarter wave length measured in the medium of the disk at a selected frequency in the operational band of the circulator. The disk is mounted on a cylindrical boss 6 that rises from the transformer plate 7. As shown in the cross-sectional view of FIG. 4, a member 8, threaded into the top wall of the waveguide. is disposed directly over the gyromagnetic disk 5. The member 8, and boss 6, preferably are of the same diameter as the gyromagnetic disks. The member 8, essentially is an extension of the waveguide top wall which permits adjustment of the gap between that wall and the gyromagnetic disk. Because of that gap, the disk is open circuited at its upper face whereas the face that lies on the boss is short cireuited. Adjustment of the gap permits tuning of the circulator. To further facilitate tuning of the device, capacitive tuning screws 9, l and 11 are provided as indicated in FIGS. 3 and 4. In each of the three waveguide arms, a capacitive tuning screw is situated above the transformer plate.

The more important dimensions to be dealt with in construction of an embodiment of the invention are indicated in FIG. 5. An embodiment of the invention of the general type shown in FIGS. 3 and 4 was constructed using WR-90 waveguide arms and a gyromagnetic element constituted of TT390 ferrite. The dimensions of that embodiment are as follows: a=.080 inch, b=.060 inch, c'=.l60 inch, d=.395 inch, and f=l.l30 inch. The dimension indicated as h in FIG. is 0.400 inch for WR-90 waveguide. That embodiment operated with a VSWR (voltage standing wave ratio) of less than l.l0 from 8.5 GH to 9.6 GH and was tuned with a capacitive screw in each arm located between the edge of the transformer plate and the ferrite disk and with the movable gap adjusting plate situated directly over the disk. Over a broader band extending from 8.0 GH, to 10.0 GH that embodiment operated with a VSWR of less than 1.30. To scale that embodiment for another frequency band. the forgoing dimensions, as a rough calculation. can be multiplied by the factor 9.05/0, where Q is the center frequency of the new band. In addition, a ferrite material should be selected whose magnetization is close to the magnetization of TT390 ferrite multiplied by the factor (1)905.

FIGv 6 shows an embodiment of the invention that is an improvement upon the FIG. 4 circulator. In the FIG. 6 circulator the ferrite disk I2 is mounted on a boss 13 that can be moved to adjust the gap between the disk and the upper waveguide wall. The boss is provided with threads that mate with threads on the transformer plate 14 whereby upon rotation of the boss, it moves vertically as viewed in FIG. 6. Extending downwardly from the upper waveguide wall is a tuning post 15 situated over the center of the ferrite disk. The tuning post is threaded into the waveguide wall to permit vertically movement of the post. The tuning post is a thin, electrically conductive rod whose presence in the guide affects only the in-phase mode of the circulator.

It has been established that circulator action depends upon the relationship between the responses of the junction to three modes supported in the junction, viz., an in-phase mode and two countenrotating modes, the reflection coefficients of which must be mutually displaced in phase by I20". The variations in bandwith exhibited by different forms of circulators depend upon the degree to which a particular structure maintains the requisite phase relation as frequency is changed and by the onset of higher order modes.

The tuning post 15 permits the in-phase mode to be tuned independently to cause its reflection coefficient to be displaced by with respect to the other modes. The in-phase mode has an electric field on the axis of symmetry such that the resonant frequency depends upon the penetration of the post into the waveguide. The counterrotating modes have only transverse electric fields in the axis of symmetry and hence are not affected by the post if that post is slender.

The invention causes higher order modes to be shifted upward in frequency compared to the conventional prior art circulator and thereby provides an additional advantage.

FIG. 7. depicts an embodiment of the invention employing a triangular gyromagnetic element 16 mounted on a triangular boss 17 rising from the triangular transformer plate 18. A tuning post 19, similar to the post of 15 of FIG. 6, is disposed directly over the center of gyromagnetic element. While not illustrated in the figure, capacitive tuning screws can be provided in each of the waveguide arms.

While not illustrated, a mixture of triangular and circular elements can be employed at the circulators junction. For example, the transformer plate may be triangular and the gyromagnetic element may be a disk disposed on a cylindrical boss.

Although the invention has been illustrated as em bodied in a symmetrical y-junction waveguide circulator, it can also take other forms such as a t-junction waveguide circulator. In view of the different forms that the invention can take, it is not intended to limit the invention to the precise embodiments illustrated in the drawings.

I claim:

1. In a three-port waveguide circulator of the type having 1. three waveguide arms meeting at a common junction, 2. an electrically conductive pedestal situated at the junction and extending into the junction from one waveguide wall, 3. a gyromagnetic element mounted on the pedestal with one face of the gyromagnetic element shortcircuited by the pedestal and the other face spaced from the opposite waveguide wall by a dielectric gap, and 4. means to establish a magnetic field of an intensity that affects the gyromagnetic action of the gyromagnetic element, the improvement wherein a. the gyromagnetic element is centrally situated at the waveguide junction and is substantially one quarter wavelength long at a frequency within the operational band of the circulator, the wavelength being the length in the guide, and the one quarter wavelength being measured at the junction along the extended longitudinal axis of a waveguide arm, and

b. the pedestal extends from an impedance transformer plate disposed upon said one wall, the impedance transformer plate effecting a reduction in the internal height of the waveguide.

2. The improved three-port waveguide circulator according to claim 1, wherein c. the gyromagnetic element is a circular disk and said one quarter wavelength is measured along the diameter of the disk, cl. the pedestal is a cylinder of the same diameter as the circular disk, and 5 e. a circular plate is disposed directly over the gyromagnetic disk and is movably mounted in the wavelength wall for adjustment of the dielectric gap. 3. The improved three-port circulator according to 10 claim 1, wherein the improvement further includes c. an electrically conductive slender post extending from said opposite wall of the waveguide into the dielectric gap, the post affecting the in-phase mode without appreciably affecting the counterrotating modes. 4. The improved three-port waveguide circulator ac cording to claim 1, wherein c. the gyromagnetic element is a circular disk and the aforesaid one quarter wavelength is measured along the diameter of the disk, d. the pedestal is a cylinder of the same diameter as the circular disk, and e. the cylinder is movably mounted whereby the dielectric gap can be adjusted by extension or retraction of the cylinder relative to said opposite waveguide wall. 

1. In a three-port waveguide circulator of the type having
 1. three waveguide arms meeting at a common junction,
 2. an electrically conductive pedestal situated at the junction and extending into the junction from one waveguide wall,
 3. a gyromagnetic element mounted on the pedestal with one face of the gyromagnetic element short-circuited by the pedestal and the other face spaced from the opposite waveguide wall by a dielectric gap, and
 4. means to establish a magnetic field of an intensity that affects the gyromagnetic action of the gyromagnetic element, the improvement wherein a. the gyromagnetic element is centrally situated at the waveguide junction and is substantially one quarter wavelength long at a frequency within the opErational band of the circulator, the wavelength being the length in the guide, and the one quarter wavelength being measured at the junction along the extended longitudinal axis of a waveguide arm, and b. the pedestal extends from an impedance transformer plate disposed upon said one wall, the impedance transformer plate effecting a reduction in the internal height of the waveguide.
 2. an electrically conductive pedestal situated at the junction and extending into the junction from one waveguide wall,
 2. The improved three-port waveguide circulator according to claim 1, wherein c. the gyromagnetic element is a circular disk and said one quarter wavelength is measured along the diameter of the disk, d. the pedestal is a cylinder of the same diameter as the circular disk, and e. a circular plate is disposed directly over the gyromagnetic disk and is movably mounted in the wavelength wall for adjustment of the dielectric gap.
 3. The improved three-port circulator according to claim 1, wherein the improvement further includes c. an electrically conductive slender post extending from said opposite wall of the waveguide into the dielectric gap, the post affecting the in-phase mode without appreciably affecting the counterrotating modes.
 3. a gyromagnetic element mounted on the pedestal with one face of the gyromagnetic element short-circuited by the pedestal and the other face spaced from the opposite waveguide wall by a dielectric gap, and
 4. The improved three-port waveguide circulator according to claim 1, wherein c. the gyromagnetic element is a circular disk and the aforesaid one quarter wavelength is measured along the diameter of the disk, d. the pedestal is a cylinder of the same diameter as the circular disk, and e. the cylinder is movably mounted whereby the dielectric gap can be adjusted by extension or retraction of the cylinder relative to said opposite waveguide wall.
 4. means to establish a magnetic field of an intensity that affects the gyromagnetic action of the gyromagnetic element, the improvement wherein a. the gyromagnetic element is centrally situated at the waveguide junction and is substantially one quarter wavelength long at a frequency within the opErational band of the circulator, the wavelength being the length in the guide, and the one quarter wavelength being measured at the junction along the extended longitudinal axis of a waveguide arm, and b. the pedestal extends from an impedance transformer plate disposed upon said one wall, the impedance transformer plate effecting a reduction in the internal height of the waveguide. 